java - in.next() 在做什么？

Question

I am using Scanner class to take input. I am trying to get all the words in a line using in.next(). I know it can be done using nextLine() but i want to understand how in.next() and in.hasNext() works.

System.out.println("What is designation");
        String desg = in.next();      
        while(in.hasNext()){
            desg+=in.next();      
        }

给出输出为

What is designation
member technical staff\n
^Z
Hello abhishek kumarNext year you will be 22Salary is 30000.0Designation is membertechnicalstaff

但是如果我使用

System.out.println("What is designation");
        String desg = in.next();      
        if(in.hasNext()){
            desg+=in.next();      
        }

它的输出为

What is designation
member technical staff
Hello abhishek kumarNext year you will be 22Salary is 44254.0Designation is membertechnical

In the first case i am getting all the words but it keeps asking for next input and i have to specify end of input using CTRL+Z. But in second case i am not getting the last word(staff). Please explain.

Answer 1

第一个代码在 while 循环中读取输入 - 即直到找到 in.hasNext() == false。

第二个代码使用 if 条件 - 它最多读取 in.next() 一次(在初始读取之后)。

因此，第二个代码并不是“等待新输入”，因为它只要求 in.next() 一次，并且直到输入耗尽为止，这与第二个代码快照不同。

<小时/>

附注请注意，String desg = in.next(); 行(在第一个代码快照中)是一种不好的做法，原因有两个:

1. 如果输入为空，则会失败。
2. 这是与 while 循环内容重复的代码。